Hi John, I'm sorry for you loss. What a loving tribute you're doing, in finishing his quilt idea!
I don't understand why you're needing it so thick either. Oh - are you talking about 'width'?
But to sew it onto the quilt, just iron the edges of your circle under about 1/4 of an inch or so, and pin it onto your quilt top, making sure it's lying good and flat, and sew it on. Make sure you have it pinned very good, due to it's large size.
If this doesn't help at all, keep asking, I'm sure someone on here will be able to explain better!
:) :)